Contents

History

Practice approach

Slapdown

The National Aeronautics and Space Administration (NASA) and the
Federal Aviation Administration (FAA) conducted a joint program for
the acquisition, demonstration, and validation of technology for
the improvement of transport aircraft occupant crash survivability
using a large, four-engine, remotely piloted transport airplane in
a controlled impact demonstration (CID). The CID program was
conducted at the Dryden Flight Research Facility of NASA Ames
Research Center (Ames-Dryden), at Edwards, California, and was
completed in late 1984. The objectives of the CID program were to
demonstrate a reduction of postcrash fire through the use of
antimisting fuel, acquire transport crash structural data, and to
demonstrate the effectiveness of existing improved seat-restraint
and cabin structural systems.[1]:1

The additive FM-9, a high molecular-weight long chain polymer, when blended with Jet-A fuel,
forms antimisting kerosene (AMK). AMK had demonstrated the
capability to inhibit ignition and flame propagation of the
released fuel in simulated impact tests.

In addition to the AMK research, NASA Langley Research Center was
involved in a structural loads measurement experiment which
included having instrumented dummies filling the seats in the
passenger compartment. Before the final flight on December 1, 1984,
more than four years of effort passed trying to set-up final impact
conditions considered survivable by the FAA.

AMK cannot be introduced directly into a gas turbine engine due to several possible
problems such as clogging of filters. The AMK must be restored to
almost Jet-A before being introduced into the engine for burning.
This restoration is called "degradation" and was accomplished on
the 720 using a device called a "degrader". Each of the four Pratt & Whitney JT3C-7 engines had a
"degrader" built and installed by General Electric (GE) to break down
and return the AMK to near Jet-A quality.

Over a series of 14 flights, General Electric installed and
tested four degraders (one on each engine); and the FAA refined AMK
(blending, testing, and fueling a full size aircraft). During the
flights the aircraft made approximately 69 approaches, to about
150 feet (46 m) above the prepared crash site, under
remote control. These flights were used to introduce AMK one step
at a time into some of the fuel tanks and engines while monitoring
the performance of the engines. During those same flights, NASA
Dryden also developed the remote piloting techniques necessary for
the 720 to fly as a drone aircraft. An initial attempt at the full
scale test was scrubbed in late 1983 due to problems with the
uplink connection to the 720. If this failed, the ground based
pilot would no longer have control of the aircraft.

Test

Pre-impact

On the morning of December 1, 1984, a remotely controlled Boeing 720
transport took off from Edwards Air Force Base, California, made a
left-hand departure and climbed to an altitude of 2,300 feet
(700 m). The aircraft was remotely flown by NASA research
pilot Fitzhugh Fulton from the NASA Dryden
Remotely Controlled Vehicle Facility. All fuel tanks were filled
with a total of 76,000 pounds (34,000 kg) of AMK and all
engines ran from start-up to impact (the flight time was 9 minutes)
on the modified Jet-A. It then began a descent-to-landing to a
specially prepared runway on the east side of Rogers Dry Lake.
Final approach was along the roughly 3.8-degree glideslope. The landing gear remained
retracted.

Post-impact 1

Passing the decision height of 150 feet (46 m) above
ground level (AGL), the aircraft was slightly to the right of the
desired path. The aircraft entered into a situation known as a
"Dutch Roll". Slightly above that decision point at which the pilot
was to execute a "go-around", there appeared to be enough
altitude to maneuver back to the centerline of the runway. The
aircraft was below the glideslope and below the desired airspeed.
Data acquisition systems had been activated, and the aircraft was
committed to impact. It contacted the ground, left wing low, at
full throttle, with the aircraft nose pointing to the left of the
centerline.

Post-impact 2

It was planned that the aircraft would land wings-level and
exactly on the centerline during the CID, thus allowing the fuselage to remain intact as
the wings were sliced open by eight posts cemented into the runway
(called "Rhinos" due to the shape of the "horns" welded onto the
posts). The throttles were to be set to idle. The Boeing 720 landed
askew. One of the Rhinos sliced through the number 3 engine, behind
the burner can, leaving the engine on the wing pylon (which does
not typically happen in an impact of this type). The same rhino
then sliced through the fuselage, causing a cabin fire when burning
fuel was able to enter the fuselage. The cutting of the number 3
engine and the full throttle situation was significant as this was
outside the test envelope. The number 3 engine continued to
operate, degrading the fuel and igniting it after impact, providing
a significant heat source. The fire and smoke took over an hour to
extinguish. The CID impact was spectacular with a large fireball
created by the number 3 engine on the right side, enveloping and
burning the 720 aircraft. From the standpoint of AMK the test was a
major set-back. For NASA Langley, the data collected on
crash-worthiness was deemed successful and just as important.

Findings

Post-impact 3

The actual impact demonstrated that the antimisting additive
tested was not sufficient to prevent a post-crash fire in all
circumstances, though the reduced intensity of the initial fire was
attributed to the effect of AMK.[2]:20–22

FAA investigators estimated that 23% to 25% of the aircraft's
full complement of 113 people could have survived the crash. Time
from slideout to complete smoke obscuration for the forward cabin
was five seconds; for the aft cabin, it was 20 seconds. Total time
to evacuate was 15 and 33 seconds respectively, accounting for the
time necessary to reach and open the doors and operate the slide.
Investigators labeled their estimate of the ability to escape
through dense smoke as "highly speculative".[2]:39–40

As a result of analysis of the crash, the FAA instituted new
flammability standards for seat cushions requiring the use of
fire-blocking layers, which performed better than conventional seat
cushions in the resulting blaze[2]:33 They also
implemented a standard requiring floor proximity lighting to be
mechanically fastened, due to the apparent detachment of two types
of adhesive-fastened emergency lights during the impact.[2]:38 Federal
aviation regulations for flight data recorder sampling
rates for pitch, roll and acceleration were found to be
insufficient.[2]:39